Fog reduction of photographic silver halide emulsions by incorporation of a nitrocinnamic acid,or cinnamaldehyde in a contiguous layer

ABSTRACT

LIGHT-SENSITIVE SILVER HALIDE EMULSIONS STABILIZED AND MADE RESISTANT TO FOGGING WITH A CINNAMIC ACID OR CINNAMALDEHYDE.

United. States Patent 3,690,181 Patented Aug. 17, 1971 FOG REDUCTION OF PHOTOGRAPHIC SILVER HALIDE EMULSIONS BY INCORPORATION OF A NITROCINNAMIC ACID, R CINNAMALDE- HYDE IN A CONTIGUOUS LAYER Giacomo Luciani and Fritz Dersch, Binghamton, N.Y.,

assignors to GAF Corporation, New York, N.Y.

No Drawing. Continuation-impart of application Ser. No. 594,675, Nov. 16, 1966. This application July 10, 1967, Ser. No. 652,003

Int. Cl. G03c 1/34 US. Cl. 96--109 18 Claims ABSTRACT OF THE DISCLOSURE Light-sensitive silver halide emulsions stabilized and made resistant to fogging with a cinnamic acid or cinnamaldehyde.

This application is a continuation-in-part of copending application Ser. No. 594,675, filed Nov. 16, 1966.

This invention relates in general to photography and in particular to the provision of novel antifogging and stabilizing compounds for use in connection with the preparation and/or processing of photographic silver halide emulsions.

It is well known that light-sensitive materials such as gelatin silver halide emulsion exhibit a marked tendency to fog. The term fog as used in the photographic art connotes that portion of the density obtained upon development which arises by virtue of factors other than the photographic exposure. The fog may be attributable to a number of influences including, for example, excessive ripening of the emulsion, prolonged storage of the film and especially under conditions of elevated temperature and/or humidity, as well as by prolonged development of the exposed emulsion, etc.

Resort to rapid-developing operations which usually require the use of elevated temperatures likewise presents severe problems of fog.

As is well known, it is conventional practice in the photographic art to incorporate into silver halide emulsions various types of sensitizing agents in order to enhance their sensitometric response. For example, gold or sulfur sensitizing agents or combinations of both have been extensively employed for such purposes. Invariably, however, prior attempts to achieve ultimate speed in photographic emulsions so sensitized have been to a large extent vitiated by the concomitant occurrence of fog.

Furthermore, similar fogging problems are encountered when employing sensitizers of the reduction type, such sensitizing agents usually being employed to augment the sensitizing properties of gold, sulfur and the like. As examples of compounds known to function as reduction sensitizers in silver halide emulsions there may be mentioned in particular the following: imino-amino-methane sulfinates; hydrazine and hydrazine derivatives; certain amines such as diethylenetriamine, triethylenetetramine, triethanolamine, silene compounds having a silocon-hydro gen bond, spermine, sodium formaldehyde sulfoxolate, stannous chloride, alkali metal sulfite; sugars, such as lactose, dextrose, ascorbic acid and the like. However, like many of their predecessors, the use of the aforementioned compounds has likewise been encumbered by severe fogging problems and especially when employed in the preparation of photographic silver halide emulsions of the high-speed type.

The foregoing problems have in many instances necessitated resort to the use of antifoggant compounds such as benzotriazole, nitro-benzimidazole, phenylmercaptotetrazole and the like. However, these particular compounds have been ascertained to provide somewhat sub-optimum results since, while serving as effective antifoggants, they display a pronounced tendency to reduce emulsion speed. To a great extent, the depression on emulsion sensitivity has more than offset any possible benefits arising from their use.

Considerable investigation likewise indicates that the gelatin itself may be a source of fogging problems. Quite obviously, the use of gelatins which are not properly balanced with regard to their content of sensitizing, restraining and anti-fogging substances frustrates attempts to alleviate the fogging problem. Despite the fact that the manufacturers of photographic gelatins are, for the most part, highly skilled in controlling the proper content of sensitizers, antifoggants, etc., e.g., by careful selection and treatment of raw materials, bones and hides, as well as the careful control of the acid or alkaline treatment of the extraction of gelatin, and selection of filter aids, it is nevertheless frequently experienced that the gelatin material remains a causal factor with regard to fog. While the substantial majority of commercial gelatins have been ascertained to be oifensive in this regard, the fogging problem has been found to be highly manifest with pigskin, chicken feet and rabbit skin type gelatins and especially when utilized in the preparation of emulsions of the ammonia type. Of the aforementioned gelatin substances, it has been ascertained in practice that the provision of pigskin-based gelatin having the requisite resistance to fog presents a particularly severe problem.

Photographic silver halide emulsions are usually provided with one or more speed-increasing agents, e.g., the polyoxyalkylenes and derivatives thereof for purposes of compensating for the depression in sensitometric response caused by the antifoggent. However, the net result has often been a reestablishment of the fogging problem.

The fogging problem is also aggravated by the use of hardening agents for the photographic emulsion, e.g.,,

formaldehyde, glyoxal, etc.

In accordance with the discovery forming the basis of the present invention, it has been found that the antifogging and stabilization characteristics of light-sensitive silver halide emulsions can be synergistically modified to advantage by the utilization of a particular class of chemical compounds in connection with the preparation of gelatin compositions contemplated for use in fabricating photographic silver halide emulsions.

Thus, a primary object of the present invention resides in the provision of improved antifogging and stabilizer compounds in which the foregoing and related disadvantages are eliminated or at least mitigated to a substantial degree.

Another object of the present invention resides in the provision of a process for the preparation of gelatin coating compositions particularly and beneficially adapted for use in the formulation of photographic silver halide emulsions characterized by high fog-resistance, improved speed, contrast, etc.

A further object of the present invention resides in the provision of gelatin coating compositions having incorporated therein a stabilizer compound which is substantially devoid of any tendency to reduce the sensitivity of photographic emulsions prepared therewith to light of longer wavelength due to the presence of one or more sensitizing dyes.

Other objects and advantages of the present invention will appear hereafter as the description proceeds.

The attainment of the foregoing and related objects is made possible in accordance with the present invention which in its broader aspect include the provision of a process for the preparation of inertized gelatin advantageously adapted for use in the preparation of photo graphic silver halide emulsions said process comprising effecting the digestion of an aqueous gelatin solution in the presence of a compound of the following structural formula:

wherein R is selected from the group consisting of and and-wherein 12 represents 1 or 2 and thereafter chilling the gelatin medium.

In said application Ser. No. 594,675 there is described the preparation of light-sensitive compositions as well as photographic elements fabricated therewith utilizing compounds of the above illustrated structural formula. As mentioned in such co-pending application, such compounds permit the realization of significant reductions in emulsion fogging in the total absence of deleterious effect upon other and vital properties such as speed, contrast, etc.

The present application is specifically concerned with the use of the identical compound in gelatin pre-treating operations whereby to render the gelatin material even more suitable for photographic use. Thus, it is found that optimum realization of the fog-suppressing effects characterizing the stabilizer compounds described herein can be achieved according to a pre-treating operation, i.e., prior to the addition of the silver halide forming ingredients, whereby the raw gelatin in aqueous solution is digested in the presence of a novel stabilizer material. Moreover, such a procedure is found to minimize to an extent heretofore considered unattainable any possibility of deleteriously affecting the ultimate light-sensitive silver halide composition.

Without intending to be bound by any theory, the following hypothesis has nevertheless been postulated in explanation of the improved results characterizing the procedure described herein. As is well known, gelatin is an organic material which is obtained from natural sources and frequently tendency for the gelatin material to vary considerably from batch to batch as regards content of active ingredients, e.g., active sulfur sensitizers. As a direct result, there is a corresponding tendency for the properties of the gelatin material to vary in some instances within intolerably wide limits. This may be due for example to variations in the content of active sulfur sensitizers. The situation becomes further problematical since in many instances the exact composition of the gelatin material in terms of quantity of sensitizer substance present is not readily determinable at least with the desired degree of accuracy.

As a direct consequence of the foregoing situation, a wide variety of techniques have been promulgated in the art involving as an essential operation the desensitization of the gelatin material whereby to render it photographically inert. The requisite degree of desensitization can be accomplished according to the methods which are essentially chemical or physical in nature. Although the improvement made possible by such techniques has in many instances been meritorious, their implementation has nevertheless been attended by one or more significant disadvantages tending to vitiate commercial feasibility. For example, physical methods based upon prolonged washing of the gelatin material invariably involve the inherent disadvantage that the lower molecular weight constituents of the gelatin are removed by extraction. The necessary consequence is of course an undesired change or shift in the physical and perhaps chemical properties of the gelatin product. Other gelatin pre-treatments involving for example the use of adsorbents although accomplishing in satisfactory manner the removal of sensitizing ingredients,

present the distinct disadvantage that undesired removal of other and vital ingredients of the gelatin medium occurs, e.g., the removal of restrainers thereby resulting in deleterious alterations of the characteristics of the gelatin. In addition, the vast majority of the methods heretofore provided are highly disadvantageous from an economic standpoint since the improvement realized by utilization of such gelatin desensitization techniques fails to justify the added cost increment involved. In a similar vein, the chemical methods thus far proposed for accomplishing gelatin desensitization have customarily proved unfeasible for one or more reasons. For example, such methods may involve the pre-treatment of the gelatin material with an oxidizing agent such as hydrogen peroxide, a peroxy acid or the like. In any event, the oxidizing agent must be present in excess to assure complete destruction of the sensitizer. Such excess can be removed upon completion of the treatment by use of a reducing agent such as a sulfite.

Although treatments of a chemical nature have proved acceptable for certain industrial applications, several objectionable tendencies have nevertheless been noted. For example, chemical treatments usually result in undesired modification of the chemical and physical properties of the gelatin substance; thus, undesired shifts may well occur in one or more of such properties as isoelectric point, setting point, viscosity, etc. Such changes are usually indicative of the fact that the protein molecule had undergone at least a partial degradation. Such deleterious effects unavoidably manifest themselves in the coated layers of which the gelatin material constitutes an ingredient.

Gelatin pre-treatments of a chemical nature present a further and significant disadvantage that complete removal of the excess of oxidizing agent is imperative. This is accomplished customarily by the employment of a small excess of sulfite ion; as will be apparent, gelatin materials which have been inertized in this manner characteristically exhibit an unusually high concentration of sulfite which of course is photographically active. Thus procedures of this nature are largely self-defeating.

In contradistinction, the compounds contemplated by the present invention for the pre-treatment of gelatin whereby to accomplish the requisite degree of inertization are uniformly characterized in possessing the singular advantage that the rather stringent techniques mandatory in the practice of prior art methods of aforedescribed type are avoided. Moreover, such compounds possess the unique advantage that the sensitometric characteristics of silver halide emulsion compositions are in no way adversely affected by the presence of such compounds; in fact, quite the contrary is true since such compounds are ascertained to be promotive of sensitivity, speed, resistance to fogging, etc.

As particular examples of compounds falling within the ambit of the present invention there may be mentioned in particular the following:

CH=CH-CH O o Ni trocinn'amaldehyde m-Nitl ocinnamaldehyde OH=CHOH 0 p-Nitrocinuamaldehyde o-Nitr-ocinnramic acid OH=GHC O OH p-Ni trocinnamic acid cinnarnic acid The novel stabilizer compounds of the present invention can be prepared according to well known techniques For example, the preparation of the nitrocinnamrc ac1ds is described in Bellstein, vol. 9, pp- 604-606; the preparation of the nitro cinnamaldehyde is described in Organic Synthesis, vol. 33, p. 60.

The compounds of the present invention may be effectively employed in concentrations varying over a relatrvely wide range. In any event, optimum realization of the 1mprovements described herein can be obtained by the M111- zation of such compounds in concentration ranging from 50 parts to about 2500 parts by weight per 1 10 parts of gelatin.

The following examples are given for purposes of 1111.18- trating the present invention in greater detail and are not to be considered in any way as being limitatlve thereof.

EXAMPLE I (A) A high speed negative ammonia emulsion was prepared using the formula described on page 332, Photographic Chemistry, vol. 1, by Pierre ilafkldes (1958). A pigskin gelatin was used. This emulslon was called (a). A second emulsion (b) was prepared which dlffered from emulsion (a) in that we used, in the second ripening (after washing) 1 cc. of a 5% solution of o-mtrocmnamaldehyde in N-methyl-Z-pyrrolidone.

These emulsions were then readied for coating on film base, that is, melted at 40 C., necessary coating finals were added, such as stabilizers 'and hardeners. Emulsion samples were coated on a suitable cellulose ester base and dried. Samples of these film coatings were then exposed m a Type I-B sensitomer and developed 1n a developer of the following composition:

Grams Metol 1.5 Sodium sulfite, anhydrous 45 Sodium bisulfite 1 Hydroquinone 3 Sodium carbonate, monohydrated 6 Potassium bromide a 0.8 Water to make 1 liter.

The sensitometric results were as follows:

Emulsion Relative speed Fog 12' dev. (a) 100 .25 (b) 100 .12

(B) Part A is repeated except that preliminary digestion of the gelatin material in the presence of the o-nitrocinnamaldehyde prior to addition of the silver halide forming ingredients as well as conventional emulsion addenda. Following preparation of the light-sensitive silver halide emulsion composition utilizing the pre-treated gelatin material coating, exposure and development are elfected as described in Part A. Similar results are obtained as regards speed and resistanceto fogging. In fact, the results obtained establish that even further improvement is realized.

EXAMPLE II Example I is repeated except that p-nitrocinnamic acid is employed in lieu of o-nitrocinnamaldehyde. Similar results are obtained as regards improved speed and resistance to fogging.

EXAMPLES III-VI Example I is repeated except that in each case the o-nitrocinnamaldehyde is replaced with equivalent amount of the following:

Example No.:

III m-Nitrocinnamic acid. IV o-Nitrocinnamaldehyde. V Cinnamaldehyde. VI Benzaldehyde.

In each of the above examples, the gelatin pretreatment operation provides an ultimate light-sensitive silver halide composition characterized by outstanding speed and resistance to fogging. Moreover, the sensitometric characteristics of the emulsion composition were in no way adversely affected and thus such properties as contrast, density, gamma and the like were eminently satisfactory.

The present invention has been disclosed with respect to certain preferred embodiments thereof, and there will become obvious to persons skilled in the art various modifications, equivalents or variations thereof which are intended to be included within the spirit and scope of this invention.

What is claimed is:

1. A gelatin coating composition for use in association with photographic silver halide emulsions comprising (a) gelatin, and (b) a fog-suppressing amount of an additive comprising a compound of the following structural formula:

wherein R is selected from the group consisting of R (i0H 2. A composition according to claim 1 wherein said additive comprises o-nitrocinnamaldehyde.

3. A composition according to claim 1 wherein said additive comprises p-nitrocinnamic acid.

and

4. A composition according to claim 1 wherein said additive comprises m-nitrocinnamic acid.

5. A composition according to claim 1 additive comprises o-nitrocinnamic acid.

6. A composition according to claim 1 additive comprises m-nitrocinnamaldehyde.

7. A composition according to claim 1 additive comprises p-nitrocinnamaldehyde.

8. A composition according to claim 1 additive comprises cinnamaldehyde.

9. A process for the preparation of a gelatin coating composition for use in association with photographic silver halide emulsions which comprises digesting an aqueous solution of gelatin in the presence of a fog-suppressing amount of a compound of the following structural formula:

wherein said wherein said wherein said wherein said -OH=CHR wherein R is selected from the group consisting of l? -COH and l LH and wherein n represents 1 or 2 when R is and wherein n represents 2 when R is 10. A composition according to claim 1, wherein said gelatin is pigskin gelatin.

11. A process according to claim 9, wherein said gelatin is pigskin gelatin.

12. A process according to claim 9 wherein said compound is o-nitrocinnamaldehyde.

13. A process according to claim 9 wherein said compound is p-nitrocinnamic acid.

14. A process according to claim 9 wherein said compound is m-nitrocinnamic acid.

15. A process according to claim 9 wherein said compound is o-nitrocinnamic acid.

16. A process according to claim 9 wherein said compound is m-nitrocinnamaldehyde.

17. A process according to claim 9 wherein said compound is p-nitrocinnamaldehyde.

18. A process according to claim 9 wherein said compound is cinnamaldehyde.

References Cited Chem. Abstract, vol. 57, 335b.

NORMAN G. TORCHIN, Primary Examiner R. E. FIGHTER, Assistant Examiner US. Cl. X.R. 106125; 260-117 

